The present invention relates to a pulsed ultrasonic flowmeter, i.e., a Doppler flowmeter, used in the fields of clinical medicine, underwater measurement, and the like, and more particularly to a flowmeter which is effective for the measurement of the blood flow in the heart.
Generally, the method of measuring the velocity of an object based on the Doppler shift of the reflected sound wave detects the component of velocity in the sound wave beam direction. In contrast, the method described in publication: Japanese Journal of Medical Ultrasonics, 40-A-56 (May 1982), pp. 395-396, calculates vectorial components of velocity from measured values based on a plurality of probes by utilization of the intersecting angle of beam.
However, the above-mentioned conventional technique bases the calculation on the measured velocities, providing only a mean value of velocity in the case of measurement of velocity in distribution, and it is not possible to calculate the spatial distribution of the flow direction.
A method of measuring the velocity at right angle with the ultrasonic beam was unveiled in an article entitled "Transverse Doppler Summary" by V. L. Newhouse. This method detects a reflected wave from the measurement position with a transducer having a wide aperture which covers the measurement position in a relatively wide angle, and evaluates the flow rate in the transverse direction from the frequency spectrum of the detected signal. However, this method can not distinguish the heading of flow in the transverse direction, i.e., the polarity of velocity. Moreover, expansion of spectrum can be caused also by existence of particles staying from main flow, and the accuracy of flow rate is not sufficient for the medical use.